The optic nerve is the part of the eye that carries visual information from the eye to the brain. The optic nerve is located at the very back of the eye just to the nose side of center. The optic nerve is the part of the eye that gets damaged when someone has glaucoma and many other ocular diseases.
The optic nerve comprising of approximately 1 million small individual thread-like nerve fibers which originates from the retina. The fibers bend about 90 degrees as they leave the retina and enter the front of the optic nerve (referred to as the optic nerve head). Normally, there is a small crater-like depression (referred to as the cup) seen at the front of the optic nerve head. In healthy eyes, the diameter of the cup is smaller than the diameter of the optic nerve. Many years ago, it was common practice for a doctor to look at the nerve using a monocular magnification device. The image of the nerve head would resemble a cup on a saucer (or disc), hence deriving a number of terms for describing the optic nerve. Such terms or descriptors include: cup to disc ratio (CDR); cupping; cupped; full rim; rim thinning; saucerization; notching, etc.).
It is critical to monitor the shape and health of the optic nerve. This is accomplished by maintaining records that describe the appearance and shape of the optic nerve. The normal cup to disc ratio (the diameter of the cup divided by the diameter of the whole nerve head or disc) is about ⅓ or 0.3. There is some normal variation here, with some patients having almost no cup (thus having 1/10 or 0.1), whereas others have as high as ⅗ths or 0.6 as a cup to disc ratio. If a patient has a cup/disc ratio larger than ⅓, then doctors get suspicious that the cup could be getting larger than it used to be, implying the progression of a disease process.
Glaucoma can cause the cup to enlarge (actually little nerve fibers are being wiped out along the rim of the optic nerve in glaucoma). Some doctors refer to an enlarged cup/disc ratio as cupping or a cupped nerve. Glaucoma typically causes the cup to get bigger in a vertical oval type pattern, initially. However, any change in the optic nerve can be an early sign of glaucoma.
To differentiate whether a large cup is normal or glaucomatous requires the doctor to pay close attention to the rim of the nerve. Photos and other analysis of the optic nerve are extremely valuable for documentation of the nerve shape and for future comparisons. If the temporal rim of the optic nerve is very thin sloped or notched, then glaucoma is more likely and may be diagnosed.
The doctor also pays close attention to the color of the optic nerve because some other diseases of the optic nerve can cause enlarged cups but also cause the nerve to look pale (multiple sclerosis, brain tumors, strokes, etc.).
One can take and record an image (i.e. photo) and store such image. Providing such image is limiting in that a photo does not clearly describe and identify information. A photo requires greater memory for storage.
What is desirable is a method that provides Doctors with the ability to maintain illustrated documentation and history of a patient's optic nerve.